1. Field of the Invention
The present invention relates to a method of molding a minute shape by injection molding, and an apparatus thereof.
2. Description of the Related Art
A method of molding a product having a minute uneven shape on the surface, such as an optical component by using a die has been used in recent years. However, in order to mold a product along a minute uneven shape formed on the molding surface of a die, it is necessary to inject a resin into the inside of the cavity of the die at high pressure. Therefore, a molding method is known in which the clamping operation of the die is stopped directly before the die is completely clamped, the resin is injected into the inside of the die at this stage, and thereafter the die is completely clamped to thereby mold the resin into a form in accordance with the minute uneven shape of the die. (for example, see Jpn. Pat. Appln. KOKAI Publication No. 5-8267)
According to this minute shape molding method, even when the resin injected into the cavity of the die does not spread over the cavity accurately along the minute uneven shape, it is possible to make the resin spread to the inner part of the minute uneven shape, and accurately transcribe the minute uneven shape to the product by clamping the die and by the clamping force.
However, in the molding method described above, there has been a problem that after the resin is injected into the die, the die is clamped again, and thus the molding time of the product becomes long. Further, in order to form a minute uneven shape, it is necessary to accurately set the temperature of the die, and thus the time required to heat the die that has been cooled to solidify the product to a predetermined temperature for the next molding has been long. That is, it is not desirable to heat the die partially to a high temperature in order to raise the temperature of the die within a short time. Heating of the die should be such that predetermined temperature distribution is obtained in its entirety. The molding time of the product has been long partially because of the necessity for such heating.